An investigative study of electrochemical induced fluorescence for fluorophores

Understanding and controlling the fluorescence of dye molecules is essential for many applications especially in biological imaging. Electrochemical-induced modulation of fluorescence provides the capability to non-destructively control the fluorescent emission of fluorophores, allowing new avenues to exploit for fluorescence imaging. This paper reports on the investigation of electrochemical-induced fluorescence modulation, focusing on the effect of the fluorophore chemical structure and the buffer composition. Of the twelve fluorophores investigated, it was observed that any variations in the chemical structure results in differences in how the fluorescence is modulated with potential. Our results showed that different core fluorescent structures exhibited distinctive modulation behaviours, the oxazine fluorophore (ATTO 655) was stable in the non-fluorescent configuration causing a prolonged low signal and the coumarin fluorophore (ATTO 390) possessed low response. Certain trends observed are related to the impact of the chemical structure on the fluorescence modulation with potential. For example, the low fluorescence modulation with potential for ATTO 390 suggests that the presence of the electron withdrawing -N⁺R₃ group facilitates significant modulation, while a lack of the -N⁺R₃ group results in low modulation. The unique response of ATTO 655 suggested the element at the radical site can affect the stability of the radical- and leuco-states and influence the fluorescence modulation that occurs. Additionally, the results show that buffer additives, such as oxygen scavengers and triplet quenchers, affect the fluorescence modulation either by stabilising the non-fluorescent radical or leuco-fluorophore structure, or improving photon emission. The quantitative characterisation of electrochemical fluorescence modulation behaviours for various fluorophores provides a guideline for future application of the fluorophores for sensing or imaging based on their performances.